Wind generator systems with associated tower structure are well known in the art. The status of such prior art is exemplified by a brief discussion of the following U.S. Patents.
Various types of wind responsive generators are known. For example, in 4,792,700; Dec. 20, 1988 issued to J. L. Ammons, a wind actuated rotor is disposed at the top of a single mast tower supported by guy wires. Such systems are inefficient both as to use of ground space and as to the utility of the available wind. Particularly at spots where prevailing winds exist, fields of such units may be disposed, and separate towers for each rotor limit the number of generators in such fields, increase the land costs and the tower costs per rotor. In this system, the use of a single mast tower is desirable to keep the footprint small and to keep tower costs down. However, this system is only operable at relatively modest heights of the rotor and cannot support a rotor at such heights that higher velocity winds are available, as unaffected by the shear friction with the ground at lower levels.
It has been known to cascade vertically on a single tower structure several rotors. This is advantageous in producing a smaller footprint per rotor, and in more effectively using available wind. However, it introduces much greater stresses up the tower, which are difficult to deal with, particularly with a single mast type of tower. Consider that the rotors to be effective must catch and resist the wind, thereby providing great lateral forces at up-tower locations. Since wind tower generation systems must be able to withstand high velocity gusting winds, the towers therefore need to be rugged and costly. In particular, consider the problems with a single mast type of tower, wherein lateral bending stresses in steel bracing tends to fatigue the metal. Thus, very costly and heavy tower structure is necessary to rigidly brace a tower against wind loads, and in general such systems could not be made to practically operate in the presence of higher velocity winds available at greater tower heights, particularly with the added stresses and lateral forces of wind encountering the multiple cascaded rotor generator systems spaced along the height of the tower. For example, W. D. Gillette in U.S. Pat. No. 4,087,990, May 9, 1978, departs from a single mast type tower to accommodate cascaded rotor structures. Similarly, R. Crehore in U.S. Pat. No. 4,184,084, Jan. 15, 1980, uses a multiple masted pyramid arrangement. Nevertheless, neither system could be made practically operable at significant heights and require large footprints, thus increasing costs and decreasing generating field efficiency.
As taught in U.S. Pat. No. 4,217,501; Aug. 12, 1980 by W. D. Allison, increased efficiency may be achieved by aligning rotors with the wind direction. That desirable feature is offset therein however by the low heights and necessity to use multiple supporting towers for disposal of several rotors.
A desirable feature of U.S. Pat. No. 4,134,707; Jan. 16, 1979, M. H. Ewers, is the ability to mount cascaded rotors in modular units at various tower heights. However this wind generation system is incapable of operation at any significant height above the ground, and because of a common vertical drive shaft and associated bearings has no ability to flex in the presence of high wind loads. Thus tower construction must be very rigid and expensive.
Another desirable prior art feature is outlined in U.S. Pat. No. 4,011,694; Mar. 15, 1977, F E. Langford, namely a dynamic guy wire system for balancing the lateral forces on a tower. This system is for protection of individual guy wires to prevent overloading, and thus permits smaller guy wires to be used or protects from sudden wind gusts, etc. that exceed the capacity of the individual guy wires. However, in this system a large number of guy wires is necessary to distribute the entire load, and there is no provision for the tower to flex or bend in the presence of peak loads.
While radio tower prior art exists, it cannot be deemed equivalent structure because in essence there has not been any problem in dealing with the lateral forces exerted at various tower heights by wind interaction with rotor-generator units.
In the F. G. F. Brakerbohm U.S. Pat. No. 1,034,760; Aug. 6, 1912, an articulated radio tower construction uses ball bearings resting on glass plates between each of a series of vertical mast sections individually guyed to the ground. The articulation feature is desirable in the manner later shown. However, the unequivalent differences between radio antenna masts and the very tall and highly transversely loaded electric generator towers of this invention require many different kinds of problems to be resolved. Thus, entirely new and functionally different articulation means are provided by this invention.
As described in Civil Engineering, July 1959, pp. 35-37 in the article, "Baltimore's Candelabra" by Robert S. Rowe, a tall antenna tower of about 200 meters is known in the antenna arts. However, this art could not teach those in the wind generating arts how to make an operable tower of greater heights that will bear the lateral wind forces reacting upon a plurality of rotor generators located at various heights along the tower. Nor is it feasible to construct towers as described therein, because of the necessity for workers to do so much detailed craftsmanship in assembling tower elements at great heights above the ground. Thus, no tall towers of the prior art are known which can achieve the wind power generator objectives of the present invention.
A further problem not adequately addressed in the prior art is that of maintenance of a wind powered generator system. Because of movable rotors, scheduled maintenance, such as for lubrication etc. is required in addition to maintenance required by catastrophic failure of any part of the system. Towers, and in particular single mast small footprint towers are not generally adapted to efficient and effective maintenance. The time of repair is critical also to the continuous generation of power, which should be interrupted as little as possible. This maintenance problem is amplified with greater tower heights. Consider for example, the necessity to replace rotor structure or generator structure at heights of several hundred meters above the ground. This requires special handling equipment such as cranes, which are not conventionally available for operating at such heights, and which if provided would be extremely costly.
Accordingly, it is a general object of the invention to improve the state of the wind generating art by resolving the foregoing deficiencies of the prior art and producing a more powerful and efficient generation system with small footprint adaptable to use in wind generating fields at prime locations with limited space, such as in mountain passes, and the like. Other objects, features, and advantages of the invention will be found throughout the following description, claims and accompanying drawings.